This invention relates to electrical connectors and in particular to a combined flexible circuit and RF stripline, zero insertion force connector utilizing a shape memory alloy actuator.
Many relatively large electronic systems such as a phased array surveillance radar system having an active aperture phased array antenna requires the use of a large number of active electronic modules. There is typically an electronic transmit/receive (transceiver) module behind every radiating antenna element and there may be as many as 100,000 elements for a large aperture system. The number of connectors required for RF signals, control signals and DC power distribution to each module is formidable. The weight penalties incurred with a large distribution system and its associated interconnect hardware can compromise or even negate the advantages of using integrated circuit technology to build lightweight transceiver modules. Coaxial microwave connectors have been used for decades and their performance is well characterized. However, the conventional coaxial connector is unfortunately an unwieldy interconnect technology for trying to access multiple RF connections in an electronic module that uses integrated circuit technology. In many cases the minimum physical module size is limited by the physical size of the coaxial connectors themselves even when using miniature and sub-miniature coaxial connectors.
The microwave signal interconnections only represent one-half of the interconnect dilemma. DC power and control signals are required by all microwave transceiver modules for operation, and depending on the complexity of the module design, the number of power and signal traces will typically range between 8 and 16. The power lines may be required to handle significant amounts of pulsed or CW current, up to as much as 2 amperes peak. The remaining lines are low current logic control signal lines. Like its microwave counterpart, Multipin DC connector technology, using a shielded pin/socket mating pair is a well-proven, effective and accepted means of interconnecting transceiver modules to an array backplane. Unfortunately the multipin DC connector technology imposes the safe ultimate size limiting constraints on the transceiver design. Pin spacings of 0.100" are common; pin spacing of 0.070" are non-standard but can be implemented; pin spacings of 0.050" are custom and result in high component and assembly costs. Hence, the minimum size and weight of the module may be set by the technology used to handle the interconnect and not by the actual input/output requirements. Many electronic devices employ flexible circuitry having a plurality of electrically conductive strips disposed in a parallel array which is well known. It is also advantageous when using such flexible circuitry to employ zero insertion force (ZIF) connector technology for ease of insertion and removal, minimization of contact wear and maximization the number of electrical connections that can be made.
An example of a zero insertion force connector for flat flexible cables that permits the unobstructed entrance of the flat flexible cable into its fully seated position, and then an actuator moves to physically urge the contacts against the conductor of the flat flexible cable is disclosed in U.S. Pat. No. 3,989,336, entitled "Flexible Circuit Connector Assembly," issued to Rizzio, Jr., on Nov. 2, 1976 and assigned to Molex Incorporated of Lisle, Ill.. Another example of the zero insertion force connector for flexible flat cables of various thicknesses and having conductors on one or both sides is disclosed in U.S. Pat. No. 4,718,859, "Zero Insertion Force Connector for Flexible Flat Cable," issued to Michael J. Gardner, on Jan. 12, 1988. This ZIF connector includes an actuator that is urged in a sliding manner into contact with an initial fulcrum on a base and the actuator defines a cable channel into which the flat cable can be inserted such that the cable is guided between arms of a C-shaped contacts. The actuator is then rotated about its initial fulcrum of the base, and the cable is urged into contact with anti-overstress fulcrums on the base. Continued rotation of the actuator urges the cable into the opposed arms of the contacts to make electrical connection.
Another approach to implementing a zero insertion force multiple contact connector uses an electrically actuated shape memory alloy in combination with a C-shaped spring wherein the shape memory alloy has the ability to change from a deformed shape to an original remembered shape when triggered thermally. Such a connector is described in an article entitled "Electrically Actuated ZIF Connectors Use Shape Memory Alloys," by John F. Krumme of Beta Phase, Incorporated, Connection Technology, April 1987 which discloses the use of flexible circuitry in combination with a single element shape memory actuator without the need for cryogenic apparatus to generate cryogenic temperatures for actuation as needed in prior art applications. Also, see U.S. Pat. No. 4,643,500, "Shape Memory Actuators for Multi-Contact Electrical Connectors," issued to John F. Krumme on Feb. 17, 1987, and assigned to Beta Phase, Inc. of Menlo Park, Calif. which describes a shape memory actuator to control opening and closing of opposed pairs of contacts in cam operated multi-contact zero insertion force connectors.
An integrated DC/RF connector comprising the capability of handling high density DC and control signals and also RF signals is highly desirable for application, for example, in the previously noted phased array surveillance radar system.